1. Technical Field
The invention relates to wheel end assemblies and in particular to wheel end assemblies for heavy-duty vehicles, such as tractor-trailers. More particularly, the invention is directed to an axle spindle nut assembly of a wheel end assembly for a heavy-duty vehicle, which includes a nut and a washer each formed with a sufficient number of interlocking features that secure components of the wheel end assembly on an axle spindle, such that during assembly, the possibility of over or under tightening the nut is minimized or eliminated.
2. Background Art
For many years, the heavy-duty vehicle industry has utilized wheel end assemblies which typically are mounted on each end of one or more non-drive axles. Each wheel end assembly typically includes a hub rotatably mounted on a bearing assembly that in turn is immovably mounted on the outboard end of the axle, commonly known as an axle spindle. The bearing assembly includes an inboard bearing and an outboard bearing, which often are separated by a bearing spacer. An axle spindle nut assembly secures the bearing assembly on the axle spindle, by engaging threads that are cut into the outer diameter of the outboard end of the axle spindle. In addition to retaining the position of the bearings and the spacer, the axle spindle nut assembly is used to provide the proper clamp force to compress the bearings, and any bearing spacer, to a predetermined amount.
As is well known to those skilled in the art, for normal operation of the wheel end assembly to occur, the bearing assembly and surrounding components must be lubricated with grease or oil. Therefore, the wheel end assembly also must be sealed to prevent leakage of the lubricant, and also to prevent contaminants from entering the assembly, both of which could be detrimental to its performance. More specifically, a hubcap is mounted on an outboard end of the wheel hub adjacent to and outboard from the axle spindle nut assembly, and a main seal is rotatably mounted on an inboard end of the hub and the bearing assembly in abutment with the axle spindle, resulting in a closed or sealed wheel end assembly.
While most wheel end assemblies include these general features, the design and arrangement of the hub, bearing assembly, bearing spacer, axle spindle nut assembly, hubcap, main seal, and other components, as well as the axle spindle, vary according to the specific vehicle design and its anticipated uses. For example, many prior art wheel end assemblies include an axle spindle nut assembly that includes multiple nuts and a lock washer. Such an assembly, while performing adequately in certain applications, can exhibit disadvantages associated with installation and maintenance of the proper clamp load.
More particularly, as mentioned above, the axle spindle nut assembly is used to provide the proper clamp force to compress the cones of the bearings and any bearing spacer to a predetermined amount. This is commonly referred to in the art as preloading the bearing cone and spacer group. For the purposes of convenience and clarity, reference herein shall be made to preloading of the bearing cone and spacer group with the understanding that such reference includes applications which utilize a bearing spacer, and applications which do not utilize a bearing spacer. Proper preloading of the bearing cone and spacer group helps to optimize the life of the bearings by controlling the tolerance range of the end play of the bearings. For example, if the clamp force on the bearing cone and spacer group is too low, there may be excessive end play of the bearings, which in turn creates excessive axial end play of the wheel end assembly relative to the axle spindle. Such excessive end play may allow undesirable movement of the main seal, which in turn potentially reduces the life of the main seal and the bearings. If the clamp force on the bearing cone and spacer group is too high, the bearings may effectively be over-compressed, interfering with their rotation and causing them to possibly wear out prematurely.
Axle spindle nut assemblies of the prior art include distinct disadvantages associated with proper installation of the nut assembly to provide the desired clamp force on the bearing cone and spacer group. For example, in the prior art, an axle spindle nut assembly with multiple nuts has been used to secure a wheel end assembly having standard heavy-duty vehicle stock inboard and outboard bearings and no bearing spacer. However, in these applications, proper installation of the axle spindle nut assembly on the wheel end assembly includes a complex procedure in which an inner nut of the axle spindle nut assembly is installed and torqued to a predetermined force level, and then a lock washer and an outer nut are installed and the outer nut is torqued to another predetermined level. Such a procedure is necessary to achieve an acceptable level of axial end play of the wheel end assembly relative to the axle spindle, such as about 5 thousandths of an inch. Because of manufacturing variances in thread form and the associated variation in thread lash between each of the nuts and the threads on the outboard end of the axle spindle, the procedure can often become quite complex. For example, the procedure typically involves torquing of the inner nut to a certain force level while the wheel hub is rotated, backing the inner nut off a certain distance, then re-torquing the inner nut while the wheel hub is again rotated, backing the inner nut off again, then installing the lock washer and torque the outer nut properly. Such a complex procedure undesirably increases the time and skill level involved to assemble the wheel end assembly, both during initial manufacturing and during maintenance-related servicing, which in turn increases the possibility of human error.
The use of multiple-nut axle spindle nut assemblies of the prior art to secure other types of wheel end assemblies, such as a wheel end assembly having standard heavy-duty vehicle stock inboard and outboard bearings and a bearing spacer, involve an installation procedure that typically is less complex than that described above for wheel end assemblies that do not include a bearing spacer, which is typically why a bearing spacer is employed. However, the use of a bearing spacer to simplify the procedure for installation of the axle spindle nut assembly undesirably increases the weight and cost of the wheel end assembly. In addition, to achieve an acceptable level of axial end play of the wheel end assembly relative to the axle spindle, the axle spindle nut assembly must undesirably be torqued to a high level when a bearing spacer is employed.
The use of multiple-nut axle spindle nut assemblies of the prior art to secure still other types of wheel end assemblies may create different disadvantages. More particularly, some wheel end assemblies include specialized, tight-tolerance unitized inboard and outboard bearings, which may reduce the need for a complex installation procedure for the axle spindle nut assembly, but still may require undesirably high torque on the axle spindle nut assembly to achieve an acceptable level of axial compression of the unitized bearing cone clamp group to obtain the desired bearing adjustment of the wheel end assembly. The use of unitized bearings also significantly increases the cost associated with the wheel end assembly and is therefore undesirable.
Furthermore, the use of the multiple-nut axle spindle nut assemblies of the prior art to secure any type of wheel end assembly increases the possibility of human error, such as, for example, one or more of the nuts in the axle spindle nut assembly being inadvertently torqued to an undesirable level, thereby undesirably over or under compressing the bearing cone and spacer group. For example, in certain prior art multiple nut and lock washer assemblies, the amount of torque on the inner nut is critical to proper compression of the bearing cone and spacer group, since the inner nut contacts the outboard bearing cone. However, since the outer nut is torqued after the inner nut has been torqued, over-torquing of the outer nut may cause the inner nut to loosen even if the inner nut has been properly torqued. More particularly, over-torquing of the outer nut may create excessive inboardly-directed pressure on the outboard face of the inner nut, which in turn causes the outboard thread faces of the inner nut to move inboardly, and thus away from the mating inboard thread faces on the axle spindle. Since engagement of these mating thread faces is necessary for the inner nut to securely maintain its position on the axle spindle, such separation of the thread faces can cause the inner nut to loosen, thereby under-compressing the bearing cone and spacer group.
Prior art axle spindle nut assemblies also lack means to indicate when the proper clamp load has been achieved, which is a disadvantage in some applications, such as when a relatively high level of torque on the spindle nut assembly is required. More particularly, many service shops have torque wrenches that can torque a spindle nut to a maximum level about 250 foot-pounds. When a wheel end assembly which requires that the axle spindle nut assembly be torqued above this level is being serviced, a technician typically may use the torque wrench to first torque the spindle nut assembly to 250 foot-pounds. Then, the technician typically will continue to tighten the spindle nut assembly, estimating the amount of torque being imposed on the axle spindle nut assembly, and may thus torque the nut assembly to an improper level.
Alternatively, to reach such a high torque level, the technician may use a torque multiplier to tighten the axle spindle nut assembly. A torque multiplier is a device known to those skilled in the art, and generally is accepted as being an unreliable method of developing the correct amount of torque on the nut, thereby potentially causing the technician to torque the axle spindle nut to an improper level. As described above, if the torque level is too low, the bearing cone and spacer group may undesirably be under compressed, and if the torque level is too high, the bearing cone and spacer group may undesirably be over compressed.
These disadvantages of prior art axle spindle nut assemblies make it desirable to develop an economical axle spindle nut assembly that is easy to install and remove, minimizes or eliminates the possibility of an installer over or under-torquing the nut assembly, indicates when the proper position of the nut of the spindle nut assembly has been attained, and can reduce the amount of torque required to preload the bearing cones. The present invention satisfies these needs, as will be described below.